A well-known method for automatically constructing conglomerate structures, in particular buildings, is described in patent application PI2005A000031. The method is carried out by a computer-aided apparatus, described in the same document, having a portion which can be moved according to the directions of three axes, one of which is vertical; this apparatus is suitable for laying alternate layers of inert granular material and a liquid binding material, in particular an epoxy resin or a polyurethane resin, creating a stone-like regions in predetermined points of a layer. All the process is carried out within side walls that define a closed perimeter.
A drawback of such method is the need of raising the side walls before laying the stone-like regions, and the disassembly of the walls after hardening, which requires relevant labour and transport costs due to the walls weight and encumbrance
Furthermore, the containing side walls are designed according to a maximum volume of the structure that can be built up inside them, therefore the volume of granular material required is often much more than necessary, thus increasing supply and handling costs, as well as the removal costs of the unused granular material.
Besides, during the construction process, and in particular at the end of it, an hydrostatic-like pressure acts on the walls due to the unbound granular material, which requires complexity and robust design of apparatus structural elements to bear the resulting load.
Epoxy or polyurethane resin, suitable for use as a binder, are not environmentally preferable, both for production and waste treatment reasons; besides, they lead to a flammable objectproduct, and release toxic exhaust gas and vapour, in particular in case of fire.
Resins require also a precise binder-to granular material ratio, which remarkably increases production costs of the spraying head used for laying the binder; furthermore, resins calls for accurate and frequent maintenance and cleaning operations, and for periodically replacing parts of the spraying heads, where the granular material and the binder are mixed.
Another drawback of the use of resins as binders, is the low elasticity modulus of the resultant conglomerate, which is the cause of too much deformability of the load-bearing parts of the structure, e.g. bending and tensile deformability.